Photomultiplier systems including a detector tube and a power supply unit for providing the accelerating voltage required to operate the detector tube are known in the field and exist in various forms. In one known photomultiplier system, as a detector tube, special electron tubes are used in order to amplify weak light signals, even to the point where individual photons are amplified, and to convert the same into an electrical signal. To this end, the detector tube usually contains a photocathode and a downstream secondary electron multiplier. Photons hit the photocathode and knock electrons out of the surface thereof. The released photoelectrons are accelerated in an electric field and hit further electrodes, each hitting electron knocking several secondary electrons out of the electrode surface. Thus, the number of electrons increases from electrode to electrode in a cascade-like fashion. At the end of the cascade, the electrons hit an anode and flow to ground. In this process, a voltage drop is generated across a resistance. This signal is coupled out for measurement. Typical detector tubes contain about 10 electrodes. The magnitude of the voltage pulse generated is proportional to the number of incident photons, i.e., to the intensity of the light. The required accelerating voltage is provided by a power supply unit.
Photomultiplier systems of this type are used, for example, in microscopes to detect detection light. In sensitive measurements, i.e., in measurements intended for the detection of weak light signals, it is problematic that the detector tube is often heated by the power supply unit, whereby background noise is generated in the detector tube, said background noise interfering with the measurement and reducing the detection sensitivity of the photomultiplier system.
In order to overcome this problem, the power supply unit could be disposed at a suitable distance from the detector tube to reduce the heating of the detector tube by the power supply unit. However, it is desirable that the spacing between the detector tube and the power supply unit be as small as possible to reduce measurement interference by external electrical noise and to minimize high-voltage wiring. However, the reduction in spacing in turn increases the risk for the detector tube to be heated by the power supply unit.